The present invention relates to a lasing device for generating a laser beam and, more particularly, to a lasing device applicable to a laser printer.
Lasers known in the art include a semiconductor laser. Compared to other lasers such as a gas laser, a semiconductor laser is small size and inexpensive, saves power, and allows its lasing intensity modulated linearly by means of drive current. By virtue of such advantages, the semiconductor laser is suitable for use with an optical scanning device as a light source.
An example of optical scanning devices of the type employing a semiconductor laser is shown in FIG. 1. In FIG. 1, a lasing device, generally 10, comprises a semiconductor laser 12 which is supported by a mount 14 and constantly controlled to an adequate temperature which ensures performance by means of a thermistor 16 and Peltie effect element 18, which serves as a temperature control element. These elements are surrounded by a heat-insulating member 20 to be thermally isolated from the outside. Located in front of the semiconductor laser 12 is a lens unit 22 in which a collimating lens is installed to convert divergent light issuing from the laser 12 to parallel light. While a larger numerical aperture (NA) provides a greater coupling efficiency of a coupled lens, an increase in the numerical aperture is accompanied by a decrease in the depth of a focus and, therefore, requires accurate positioning of the lens. Generally, a numerical aperture of about 0.3 is considered acceptable in in view of its relation with the focal depth.
In the prior art device 10, although the semiconductor laser 12 is surrounded by the heat-insulating member 20 and controlled in temperature, support members 24 and 26 supporting the lens unit 22 are placed in an environment which is no more than atmospheric one with respect to heat and, in addition, their temperature is not controlled and, so, directly effected by the ambient temperature.
As a result of temperature variations due to the drive of the lasing device 10 and the optical scanning device using it as well as variations of room temperature, the support members 24 and 26 undergo thermal expansion (or contraction) which in turn causes a change in the spacing between the semiconductor laser 12 and the collimating lens. Such prevents a desired imaging beam diameter from being provided on a photoconductive element or a document.